1. Field of the Invention
This invention relates to a zoom lens and, more particularly, to a zoom lens suitably used in a liquid crystal projector to magnify and project an image, e.g., image information displayed by a liquid crystal display device or the like, onto a screen.
2. Description of the Related Art
Various projection-type display apparatuses have been provided that are arranged to project an image onto a screen in such a manner that a plurality of images formed by liquid crystal light bulbs or the like, and having color information, are illuminated with predetermined color light, are optically superposed on each other, and the superposed image is projected onto the screen.
FIG. 13 is a schematic diagram of an optical system of a conventional projection display apparatus.
As shown in FIG. 13, liquid crystal display devices such as, e.g., liquid crystal light bulbs 1, 2, and 3, are provided and have surfaces on which images (black-and-white images) are formed on the basis of predetermined color information.
A light beam from a white light source 14 is separated into color light beams having colors in accordance with the color information, e.g., red (R), green (G) and blue (B), by dichroic mirrors 8 and 9. The liquid crystal light bulbs 1, 2, and 3 having images on the basis of the color information are irradiated with the corresponding color light (the color light for the liquid crystal light bulb 1 traveling via a total reflection mirror 7) by using condenser lenses 4, 5, and 6.
The light beam from the liquid crystal light bulb 3 travels to a dichroic mirror 11 through an optical path bent by a total reflection mirror 12, while the light beams from the liquid crystal light bulbs 1 and 2 travel to the dichroic mirror 11 via a dichroic mirror 10. The dichroic mirror 11 combines these light beams to form a color image on the basis of the color light of three colors, i.e., red, green and blue. The color image is projected onto a screen (not shown) by a projection lens 15.
In the projection display apparatus shown in FIG. 13, light which illuminates a peripheral portion of each of the liquid crystal display devices 1, 2, and 3 is incident upon the liquid crystal display device at a large angle. There is, therefore, a problem of a contrast non-uniformity through the display surface of each liquid crystal display device. There is also a problem of the rate of an opening area of each liquid crystal display device being reduced with an increase in the number of pixels of the liquid crystal display device.
A liquid crystal display device member has been provided that has a micro lens array 26 facing pixels 27, as shown in FIG. 14, to improve the contrast uniformity and the rate of opening area of the liquid crystal display devices.
Such a liquid crystal display device member having a micro lens array, however, entails a problem of a kind of vignetting of a light beam, such as that shown in FIG. 15, unless the light beam is incident upon the liquid crystal device approximately perpendicularly, or if the telecentricity of the projection lens is reduced.